Quasars and Answers

(Image credit: NASA/ESA/CSA/Joseph Olmsted (STScI))

Somewhere in the universe, a black hole is powering a light so intense its output is as much as a thousand times that of an entire galaxy containing a hundred billion stars. If you’ve never heard of them, let me introduce you to…the quasar.

What, you’ve never heard of a quasar? Buckle in because we’ll be traveling billions of light-years from Earth where they are found. 

Quasars were first discovered in the 1960s. At first glance, astronomers saw them as ordinary stars but they emitted such strong radio waves and light that they couldn’t quite categorize them. Today, this is what scientists have learned: they are distant galaxies whose brightness is powered by supermassive black holes. Their luminosities have been found between 10 to 100,000 times that of our Milky Way galaxy. 

So, how exactly does a black hole power a quasar? Well, let’s start with what we know about black holes. We don’t understand them fully yet but we do know that their name is a bit of a misnomer, as these objects aren’t really holes. They are massive concentrations of matter, with gravity so powerful that nothing, not even light, can escape its gravitational pull. 

Black holes grow by consuming matter, a process that scientists call accretion. If a star gets too close to it, the black hole will pull all the gas from the star and this gas settles into a hot, bright, spinning disk (accretion disk). Matter gradually works its way from the outer part of the disk to its inner edge, where it falls into the event horizon. Think of the event horizon as the surface of the black hole.  

Quasars occur when immense amounts of matter fall into a supermassive black hole, spiraling around it in the form of a disk before entering. There is such extreme gravitational and frictional force on the accretion disk that it causes the gas and dust to heat up to millions of degrees and become luminous, blasting out brilliant jets of material into the universe. The jets and the glowing disk, together, outshine their host galaxies.

Because quasars are billions of light-years from Earth, by the time we see them, we are seeing galaxies as they were in the earlier universe. And because quasars require so much matter to spark their luminosity, astronomers believe they occur when galaxies merge, which was much more frequent in the early universe.

NASA's James Webb Space Telescope has given us beautiful images of the oldest quasars, allowing us to look back more than 13 billion years ago, only 700 million years after the Big Bang. A quasar's story can teach us a lot about the origins of the universe, cluing us in to the answers to the biggest mysteries of our cosmic evolution.